Lead-acid battery failure can result from grid corrosion and separation of the active material from the plate, in particular the positive plate. This corrosion is due to self-discharge of the electrode, and to oxidationreduction reactions taking place between the plate and electrolyte during charging-discharging cycles. Lead oxides and sulfates formed as the grid corrodes are larger than lead, and result in creep or expansion of the grid. This is significant in battery manufacture, since grid growth is anticipated and provided for by leaving extra space in the casing.
Factors affecting battery life include the extent of contact between grid lead and lead dioxide, contact between plate and electrolyte, degree of plate porosity (greater porosity allows greater contact), and thickness of the grid. Generally, a lead-acid positive plate will serve about one year per ten mils of thickness. In order to extend battery life to about 20 to 30 years, a positive plate as thick as 0.31 inches has been used. This increases battery size as well as cost. A battery plate is needed which can resist self-discharge and corrosion in acid electrolyte, maintain adhesion of the active material, be manufactured economically, and diminish electrode size, but not strength or life. Such a plate would be especially suited for high power applications.
Barium metaplumbate is a metal oxide of perovskite structure commonly prepared at high temperatures of 650-1000.degree. C. by reaction of BaCO.sub.3, BaCl.sub.2, Ba(NO.sub.3).sub.2, BaO.sub.2 or BaO with PbO, PbO.sub.2, or Pb.sub.3 O.sub.4. Applications of metal oxide perovskites have focused on the superconductive properties of these compounds as described in Sleight, U.S. Pat. No. 3,932,315, issued Jan. 16, 1976 and Inagaki Japanese Patent Pub. 63-112432 (1988), which discloses compounds of the formula MPbO3, wherein M is Zn, Mn or Cd. Applications in electrical components (Penneck et al., U.S. Pat. No. 4,470,898, issued Sep. 11, 1984) and as corrosion-resistant coatings (Tada U.S. Pat. No. 4,352,899, issued Oct. 5, 1982) have been described.
Barium metaplumbate has been used in semiconductors, capacitors, and resistors, as outlined in Nitta et al., U.S. Pat. No. 3,374,185, issued Mar. 19, 1968, Hiremuth, U.S. Pat. No. 4,761,711, issued Aug. 2, 1988, Japanese Patent pub. 63-136,507, and Chemical Abstracts 106:147845v, 109:65406a, 85:18563m, 79:46649c and 79:46650w. Barium metaplumbate synthesis using Ba(OH).sub.2 and PbO at 1200 degrees to produce a powder has been reported in Chemical Abstracts 74:16428j. However, high temperature reactions for producing barium metaplumbate are energy intensive and preclude the possibility of forming a coating on a low-melting substrate such as lead.
The present invention provides an alternative process for synthesis of barium salts such as barium metaplumbate which can be carried out at a relatively low temperature, and which can thus be used to make lead-acid battery grids coated with barium metaplumbate to address the problems described above with lead-acid battery plates.